Alphanumeric display modules of the type employing light emitting diodes (LED) or liquid crystals (LCD) are now used in a number of electronic devices requiring the visual display to an observer of information generated by the operator of the device. Examples only of such devices are simple calculators, cash-registers, weigh scales, clocks and radios. Such modules consist of a fixed number of so-called "cells", each of which cells includes a number of elements that are energized selectively for the cell to display the required information, usually one numerical or alphabetical integer. Cells intended solely for display of number information now almost universally are of "figure eight" configuration, coprising seven controllable elements which when all operative cause the cell to display the numeral 8; the other nine numbers in the decimal system can be displayed by selection of fewer elements. The cell requires eight control leads, one for each element to be controlled plus one common lead, to which appropriate control voltages are applied to activate the selected cell elements.
Such a cell has a highly restricted capacity for display of alphabetical information without substantial ambiguity, and is in practice limited to the thirteen letters "A", "B", "C", "E", "F", "H", "I", "J", "L", "O", "P", "S" and "U", plus the letter "D" if the possibility of ambiguity with the letter "O" is ignored, all in upper case. The lower case availability is even more limited, being restricted to the letters "b", "c", "d", "i", "l", "n", "o", "r" and "u". Modified forms of cell that are used if alphabetical information must be displayed employ four and five more elements respectively, so that 12 and 13 electrical control lines respectively are required. In one such modified form the four additional elements form two diagonals from corner to corner, while the other modified form employs the same four diagonal elements, and in addition the middle cross-bar is divided into two separate elements. Even these modified forms are not able to clearly resolve all of the possible ambiguities, such as those between "U" and "V" and between "D" and "O".
It is also becoming a requirement to be able to present on a single display module different pieces of information alternatively and/or in some sequence, and this necessitates storage of the non-displayed information in some inexpensive manner and its subsequent retrieval from storage and employment to control the display module. The volume cost of a commercially or custom produced integrated circuit (IC) is directly related to the size of the actual silicon chip and the number of connections made from the chip to other outside circuitry. An IC that measures 100 mil by 100 mil and requires 42 external connections will be unexpectedly more expensive than an IC that only requires 38 external connections. This fact is simply because there are direct costs associated with bonding small wires from the pads on the silicon chip to the external metal pin connectors. There are also available standard IC packages that only allow for a certain number of connections; a standard 48 pin package of this type costs considerably more than a 40 pin package, and a 64 pin package is priced higher than a 48 pin package. Thus, there are significant economic advantages to first minimizing the number of connections from an IC and second to keeping the total number of connections to a value permitting use of one of the standard size packages. One standard package has 40 possible connections. In a typical display controller for a liquid crystal display (LCD) with 40 external pins, one pin must always be used as a ground, one for input voltages (5 volts), one for signal input, one for clock input, and finally one for the backplane or what might be called the ground of the display. This leaves with this package a maximum of 35 pins for direct driving and control of the display segments. This size also limits to five the number of "figure eight" cells that could be employed with a 40 pin element, and limits to three the number of modified cells, without the complications and expense of employing a non-standard storage element or a number of separate standard storage elements for each module.
A particular example of the application of such a display unit is a merchandising module for a food market which can, for example, be placed on a shelf edge in front of the respective row or rows of goods and operated to give prospective purchasers information selectively and/or in sequence as to total price per item, unit price per item, the percentage reduction of a sale price, etc. It is also desired to be able to operate the module to give different merchandising messages involving alphabetical information. Such a module and its associated control circuitry must be relatively inexpensive to be acceptable commercially in the highly cost conscious environment of food marketing, and at this time this requires that the entire module be fully operative with not more than forty control lines, so as to be operable with existing forty terminal memory storage devices. It is possible to provide all of the numerical information required with four "figure eight" cells, requiring 32 control lines. However, the module must also be able to display at least one decimal period, and alternatively the cents symbol ".cent." and the percentage symbol "%" which, since they have the oblique stroke in common, can be operated from only three more lines, for a total of 36 lines. This leaves only four control lines available to input any additional information that may be required and provide power voltages and ground.